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Key takeaways
- A ring main lets water reach any point from two directions, so one break or closed valve doesn’t isolate an area.
- Onshore ring mains are usually buried and feed hydrants and monitors.
- Offshore ring mains run on the topsides, often in corrosion-resistant materials, and feed deluge systems through deluge valves.
Why a ring main?
A firewater system must deliver water to any area of the plant at the required flow and pressure. Running the main as a loop means water can reach any point from two directions. Sectionalising valves let a damaged section be isolated without losing the rest of the system.
Onshore
- Water source: firewater tank or reservoir, with diesel-driven and electric fire pumps.
- Ring main: usually buried around the process units, in materials such as cement-lined carbon steel, HDPE or GRE, with corrosion protection for metallic pipe.
- Outlets: hydrants and fixed monitors at spacings set by the design standard, plus deluge and sprinkler systems on specific equipment such as tanks, pumps and loading racks.
- Design references: NFPA 24 for private fire service mains, NFPA 15 for water spray systems, and company standards.
Offshore
- Water source: seawater lifted by firewater pumps, often in caissons or from the hull.
- Ring main: runs on the topsides around the process modules, usually in GRE, 90/10 copper-nickel, super duplex or titanium because seawater is corrosive.
- Outlets: deluge valves for each fire area, hose reels, monitors and foam systems. Downstream of each deluge valve the pipework is normally dry until the valve opens.
- Dry deluge pipework is a known problem area: it is exposed to salt air and may corrode internally and block nozzles. Corrosion-resistant materials and periodic flushing are used to manage this.
- Fire exposure: the ring main must survive a fire long enough to supply water. GRE must be qualified for fire exposure, and dry sections usually need metallic materials.
- Design references: NORSOK S-001 technical safety, NFPA standards, and company specifications.
| Item | Onshore | Offshore |
|---|---|---|
| Water | Fresh water from a tank | Seawater |
| Ring main | Buried | On topsides |
| Typical materials | Cement-lined CS, HDPE, GRE | GRE, CuNi, super duplex, titanium |
| Main outlets | Hydrants, monitors | Deluge valves, hose reels, monitors |
| Main risk | Buried corrosion, damage | Seawater corrosion, blocked dry nozzles |
Code reference
NFPA 24 Installation of private fire service mains.
NFPA 15 Water spray fixed systems for fire protection.
NORSOK S-001 Technical safety.
ISO 14692 GRP piping, including fire performance.
What to take back to your desk
Treat the firewater ring main as a safety-critical system from day one: route it where it is least likely to be damaged by the fire it is meant to fight, and choose materials that will still work after twenty years of standing still.
Educational content. Always design to your project specification.
